From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 71F37606A324 for ; Thu, 22 Oct 2026 08:07:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=W8OWakWc Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id BAA051123D5; Thu, 22 Oct 2026 08:07:22 +0000 (UTC) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 518401123D5 for ; Thu, 22 Oct 2026 08:07:17 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 01594414E6; Thu, 22 Oct 2026 08:07:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4890C1F000C2; Thu, 22 Oct 2026 08:07:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792656436; bh=IK3vlu7wIXXSLKBylI9CXBQS+y3D6BVh2hkB8AeGdBU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=W8OWakWcVu6p39n/i/pswI3AEMxPh3lVJFQRbJlRBkHWiGvyfX0zXNVk2SA4fB53g JHz4wNXmab5xisFmoVJgNFDkp+pI303W5So1d0OPUiMMHVQJWz8xuIK2aEajORCG++ reNbr9AqxfCgM8sCBsaPNlNAtM/M7qg+ZuOxPYKUvOrJRA2PnNbcCNNvkN2coaJAdq FP7utVEamab8mGO32rjrrQwCCeXrVEPqqsXIZBlr2QOEY3hDSZgnzuU+phWNMEaN5b 82XCF3BVPJKHXalMygYHHKD5QJ+Hda5VHcVnDI/8kyvAqN7UYo8dXeht0md63zKLNg Y4d6s9egOW1PA== Date: Thu, 22 Oct 2026 09:07:09 +0100 From: "Lorenzo Stoakes (ARM)" To: Konstantin Khorenko Cc: Andrew Morton , "David Hildenbrand (Arm)" , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Peter Xu , Alex Williamson , kvm@vger.kernel.org, =?utf-8?B?TG/Dr2M=?= Molinari , Shuah Khan , linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org, Madhavan Srinivasan , "Ritesh Harjani (IBM)" , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jason Gunthorpe Subject: Re: [PATCH v4 1/4] mm/rmap: duplicate a PMD mapping as one in folio_dup_file_rmap_pmd() Message-ID: References: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-0-66f00b7a564c@virtuozzo.com> <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-1-66f00b7a564c@virtuozzo.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-1-66f00b7a564c@virtuozzo.com> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "dri-devel" X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 21, 2026 at 10:36:00PM +0200, Konstantin Khorenko wrote: > folio_dup_file_rmap_pmd() passes PGTABLE_LEVEL_PTE to > __folio_dup_file_rmap() for HPAGE_PMD_NR pages, so it adds HPAGE_PMD_NR > PTE mappings to the folio instead of one PMD mapping. Each unmap of the > PMD removes one PMD mapping: > > - the folio's mapcount never returns to zero, and removing the folio > from the page cache reports "Bad page cache", or hits a VM_BUG_ON > with CONFIG_DEBUG_VM; > - the first unmap already counts as the last one and drops the > PMD-mapped statistics while the other mm still maps the folio; > - the second one drives the entire mapcount below zero and drops them > again. > > The helper has no caller yet, the next patch adds the first one. Pass > PGTABLE_LEVEL_PMD, as folio_try_dup_anon_rmap_pmd() does. > > Fixes: d8ef5e311d7b ("mm/rmap: convert page_dup_file_rmap() to folio_dup_file_rmap_[pte|ptes|pmd]()") Was this a mistake in d8ef5e311d7b, or actually intentional for whatever reason? If the latter this shouldn't be a fixes. > Signed-off-by: Konstantin Khorenko > --- > include/linux/rmap.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index 0b332770abeed..7562017416094 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -558,7 +558,7 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio, > struct page *page, struct vm_area_struct *dst_vma) > { > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - __folio_dup_file_rmap(folio, page, HPAGE_PMD_NR, dst_vma, PGTABLE_LEVEL_PTE); > + __folio_dup_file_rmap(folio, page, HPAGE_PMD_NR, dst_vma, PGTABLE_LEVEL_PMD); > #else > WARN_ON_ONCE(true); > #endif > > -- > 2.43.0 > -- Cheers, Lorenzo